Viroid

For a variant of it which is dependent on viruses, see Virusoid.

Viroid
Virus classification Edit this classification
Informal group: Subviral agents
(unranked): Viroid
Families

Pospiviroidae
Avsunviroidae

Viroids are small single-stranded, circular RNAs that are infectious pathogens.[1][2] Unlike viruses, they have no protein coating. All known viroids are inhabitants of angiosperms (flowering plants),[3] and most cause diseases, whose respective economic importance to humans varies widely.[4] A recent metatranscriptomics study suggests that the host diversity of viroids and other viroid-like elements is broader than previously thought and that it would not be limited to plants, encompassing even the prokaryotes.[5]

The first discoveries of viroids in the 1970s triggered the historically third major extension of the biosphere—to include smaller lifelike entities—after the discoveries in 1675 by Antonie van Leeuwenhoek (of the "subvisible" microorganisms) and in 1892–1898 by Dmitri Iosifovich Ivanovsky and Martinus Beijerinck (of the "submicroscopic" viruses). The unique properties of viroids have been recognized by the International Committee on Taxonomy of Viruses, in creating a new order of subviral agents.[6]

The first recognized viroid, the pathogenic agent of the potato spindle tuber disease, was discovered, initially molecularly characterized, and named by Theodor Otto Diener, plant pathologist at the U.S Department of Agriculture's Research Center in Beltsville, Maryland, in 1971.[7][8] This viroid is now called potato spindle tuber viroid, abbreviated PSTVd. The Citrus exocortis viroid (CEVd) was discovered soon thereafter, and together understanding of PSTVd and CEVd shaped the concept of the viroid.[9]

Although viroids are composed of nucleic acid, they do not code for any protein.[10][11] The viroid's replication mechanism uses RNA polymerase II, a host cell enzyme normally associated with synthesis of messenger RNA from DNA, which instead catalyzes "rolling circle" synthesis of new RNA using the viroid's RNA as a template. Viroids are often ribozymes, having catalytic properties that allow self-cleavage and ligation of unit-size genomes from larger replication intermediates.[12]

Diener initially hypothesized in 1989 that viroids may represent "living relics" from the widely assumed, ancient, and non-cellular RNA world, and others have followed this conjecture.[13][14] Following the discovery of retrozymes, it has been proposed that viroids and other viroid-like elements may derive from this newly found class of retrotransposon.[15][16][17]

The human pathogen hepatitis D virus is a subviral agent similar in structure to a viroid, as it is a hybrid particle enclosed by surface proteins from the hepatitis B virus.[18]

  1. ^ Navarro B, Flores R, Di Serio F (29 September 2021). "Advances in Viroid-Host Interactions". Annual Review of Virology. 8 (1): 305–325. doi:10.1146/annurev-virology-091919-092331. ISSN 2327-056X. PMID 34255541.
  2. ^ Di Serio F, Owens RA, Li SF, Matoušek J, Pallás V, Randles JW, Sano T, Verhoeven JT, Vidalakis G, Flores R (November 2020). Zerbini FM, Sabanadzovic S (eds.). "Viroids". Archived from the original on December 2, 2020. Retrieved February 3, 2021.
  3. ^ Hadidi A (January 2019). "Next-Generation Sequencing and CRISPR/Cas13 Editing in Viroid Research and Molecular Diagnostics". Viruses. 11 (2): 120. doi:10.3390/v11020120. PMC 6409718. PMID 30699972.
  4. ^ Adkar-Purushothama CR, Perreault JP (August 2020). "Impact of Nucleic Acid Sequencing on Viroid Biology". International Journal of Molecular Sciences. 21 (15): 5532. doi:10.3390/ijms21155532. PMC 7432327. PMID 32752288.
  5. ^ Lee BD, Neri U, Roux S, Wolf YI, Camargo AP, Krupovic M, et al. (RNA Virus Discovery Consortium; Simmonds P, Kyrpides N, Gophna U, Dolja VV, Koonin EV) (2 Feb 2023). "Mining metatranscriptomes reveals a vast world of viroid-like circular RNAs". Cell. 186 (3): 646–661. bioRxiv 10.1101/2022.07.19.500677. doi:10.1016/j.cell.2022.12.039. PMC 9911046. PMID 36696902.
  6. ^ King AM, Adams MJ, Carstens EB, Lefkovitz EJ, et al. (2012). Virus Taxonomy. Ninth Report of the International Committee for Virus Taxonomy. Burlington, Massachusetts, US: Elsevier Academic Press. pp. 1221–1259. ISBN 978-0-12-384685-3.
  7. ^ Diener TO (August 1971). "Potato spindle tuber "virus". IV. A replicating, low molecular weight RNA". Virology. 45 (2): 411–28. doi:10.1016/0042-6822(71)90342-4. PMID 5095900.
  8. ^ "ARS Research Timeline – Tracking the Elusive Viroid". 2006-03-02. Retrieved 2007-07-18.
  9. ^ Flores R, Hernández C, Martínez de Alba AE, Daròs JA, Di Serio F (2005). "Viroids and viroid-host interactions". Annual Review of Phytopathology. 43: 117–39. doi:10.1146/annurev.phyto.43.040204.140243. PMID 16078879.
  10. ^ Tsagris EM, Martínez de Alba AE, Gozmanova M, Kalantidis K (November 2008). "Viroids". Cellular Microbiology. 10 (11): 2168–79. doi:10.1111/j.1462-5822.2008.01231.x. PMID 18764915. S2CID 221581424.
  11. ^ Flores R, Di Serio F, Hernández C (February 1997). "Viroids: The Noncoding Genomes". Seminars in Virology. 8 (1): 65–73. doi:10.1006/smvy.1997.0107.
  12. ^ Moelling K, Broecker F (March 2021). "Viroids and the Origin of Life". International Journal of Molecular Sciences. 22 (7): 3476. doi:10.3390/ijms22073476. PMC 8036462. PMID 33800543.
  13. ^ Diener TO (December 1989). "Circular RNAs: relics of precellular evolution?". Proceedings of the National Academy of Sciences of the United States of America. 86 (23): 9370–4. Bibcode:1989PNAS...86.9370D. doi:10.1073/pnas.86.23.9370. PMC 298497. PMID 2480600.
  14. ^ Moelling K, Broecker F (2021-03-28). "Viroids and the Origin of Life". International Journal of Molecular Sciences. 22 (7): 3476. doi:10.3390/ijms22073476. ISSN 1422-0067. PMC 8036462. PMID 33800543.
  15. ^ Cervera A, Urbina D, de la Peña M (2016-06-23). "Retrozymes are a unique family of non-autonomous retrotransposons with hammerhead ribozymes that propagate in plants through circular RNAs". Genome Biology. 17 (1): 135. doi:10.1186/s13059-016-1002-4. ISSN 1474-760X. PMC 4918200. PMID 27339130.
  16. ^ de la Peña M, Cervera A (2017-08-03). "Circular RNAs with hammerhead ribozymes encoded in eukaryotic genomes: The enemy at home". RNA Biology. 14 (8): 985–991. doi:10.1080/15476286.2017.1321730. ISSN 1547-6286. PMC 5680766. PMID 28448743.
  17. ^ Lee BD, Koonin EV (2022-01-12). "Viroids and Viroid-like Circular RNAs: Do They Descend from Primordial Replicators?". Life. 12 (1): 103. Bibcode:2022Life...12..103L. doi:10.3390/life12010103. ISSN 2075-1729. PMC 8781251. PMID 35054497.
  18. ^ Alves C, Branco C, Cunha C (2013). "Hepatitis delta virus: a peculiar virus". Advances in Virology. 2013: 560105. doi:10.1155/2013/560105. PMC 3807834. PMID 24198831.